NEW YORK -LRB- CNN -RRB- -- He 's only 5 1/2 years old , and yet he 's practically memorized the entire New York subway grid .

Gwenyth Jackaway started to wonder if Donor-X passed on a genetic component to her son , Dylan , who is autistic .

He reads at the fourth-grade level , plays two-handed piano compositions and is better versed than most adults about the Fibonacci code , a complex mathematics sequence .

Dylan loves Italian music and draws pictures that artist Jackson Pollock would be proud of .

He also happens to be autistic .

Gwenyth Jackaway , Dylan 's mother , is a professor at New York 's Fordham University . She 's single but had always wanted to have a child . So she contacted California Cryobank , one of the largest sperm donor banks in the country .

Cryobank does n't reveal the identities of donors but allows people to choose based on the traits they 'd like their child to have . Jackaway decided on `` Donor X '' because he appeared philosophical and intelligent on paper . He liked music , loved to travel and had a high IQ and a degree in economics .

What she could n't know then is that her son would have autism . So she started to wonder whether Donor X might carry a gene that could have contributed . Dylan tells Randi Kaye how to take subway back to work ''

The cause or causes of autism are not known and are hotly debated . Most experts believe that genetics are a component , making a child predisposed to autism or responsive to an environmental trigger .

`` It 's a combination of being genetically vulnerable and then having some kind of social or toxicant exposure that tips you over , '' according to Dr. Gary Goldstein of the Kennedy Krieger Institute .

Researchers have found some genetic areas associated with autism , but it could take years before the gene or genes that cause autism or contribute to it will be determined .

Until then , Geri Dawson , chief science officer for the Manhattan-based advocacy group Autism Speaks , says there 's no way to screen for those genes and prevent them from being passed to a child .

`` We would n't be able to screen a donor for autism because we do n't yet know the specific genes that are contributing to autism , '' Dawson said . `` But there is a lot of research going on , and I would say in the next five to 10 years , we will have identified between five and 10 genes that we know raise the risk for autism . ''

Once the autism gene or genes have been identified , it would theoretically be possible to screen for those genes , according to Dawson .

Jackaway says she went into a period of mourning when Dylan 's autism was diagnosed at age 2 .

`` When you 're handed a diagnosis of some sort of developmental disorder , you have to let go of the child you thought you were going to have , '' Jackaway said . `` There 's a sense of loss of the child , a grieving process . There 's denial , there 's rage , and then there 's the tremendous sadness , and hopefully you get to a place of accepting . ''

Jackaway says she had to accept that `` I do n't have that child I thought I was going to have . But I have this child instead , who 's right here in front of me . ''

Through a Web site called Donor Sibling Registry , she reached out to other women who used Donor X . She found six families who had used the same donor .

Two years ago , she visited Theresa Pergola in the New York area ; she had given birth to triplets using sperm from Donor X. Just minutes into their meeting , Jackaway noticed Pergola 's son , Joseph , 2 , exhibiting some of the same behavior as her son .

`` He was walking on his toes ; he was flapping his hands . There seemed to be eye contact issues , '' recalled Jackaway , who immediately suggested screening Joseph for autism .

`` She told me that she saw characteristics of autism , and it was very upsetting to me at that time , '' Pergola said . `` I did n't know what to expect from that point on . I know I was scared , and she was there to let me know that it was going to be OK . ''

Pergola says she was afraid because she had an image of autism in her head and believed her son would be `` in the corner and rocking and not talking . ''

She says Jackaway reassured her that would n't be the case .

One month later , a test confirmed what Pergola already knew : Joseph was autistic . The diagnosis brought her to tears , and now these two women whose sons share a father were immediately connected by another bond : autism .

`` She was terribly upset , '' Jackaway remembered . `` That moment is a terribly frightening moment . You get handed a diagnosis , and you get handed an entirely new future . ''

In six families Jackaway contacted that had used Donor X , three of the children are autistic , and one is showing signs of autism .

But would Jackaway be happier today if there had been a way to screen Donor X for an autism gene ?

`` I 've done a lot of thinking about this , and to say yes to that is to say that I wish Dylan is n't Dylan , '' Jackaway said . `` I love my son and everything about him , and that means loving his autism also . Loving your children means loving everything about them . Our children do n't have autism ; they are autistic . It 's part of who they are . '' There is currently no way to screen for autism , and in a statement , the company said in part :

`` There is no current genetic test to detect autism . California Cryobank -LRB- CCB -RRB- employs one of the most thorough and rigorous donor screening processes in the industry , with less than 1 % of all applicants actually becoming donors . The standard CCB procedure for screening donors involves extensive physical , genetic and health screening ... ''

Since the discovery of autism in some of the families that used Donor X , Cryobank had this to say about his samples :

'' ... per CCB policy , the donor 's samples were removed from the general catalog . These vials may only be sold to a client who has previously used specimens of this donor and is interested in ordering additional specimens . In this case the client is made aware of the new medical information and potential issues ... ''

The families do n't blame the sperm bank . In fact , Theresa Pergola says she 's still uncertain about an autism screening process , if and when it ever becomes available .

`` It can go either way , on the one hand it could be helpful so that people could make choices about what risks they want to take , '' says Pergola . `` On the other hand it 's like , what else are they going to screen for , you know ? Are they going to screen for certain personality traits ? It 's hard to say . It 's really hard to say . '' E-mail to a friend

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Gwenyth Jackaway never imagined donor could pass autism genetically to son

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Her son , Dylan , two other kids connected to Donor-X are autistic

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Expert says genetic component , environmental trigger linked to autism

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Since autism discovery , Donor X samples are no longer available for reproduction